CN107476807A - A kind of coal seam tight roof fracturing method for weakening - Google Patents

Abstract

The invention discloses a cracking and weakening method for a hard roof of a coal seam, which comprises the following steps: firstly drilling a cracking hole into the roof, and then injecting liquid nitrogen into the rock layer of the roof in a pulsating manner by using an adiabatic sleeve to prevent pulsation fatigue damage and low-temperature cold shock of liquid nitrogen The coupling effect of the coupling can greatly weaken the strength of the roof rock formation itself. When the gasification pressure exceeds the tensile strength of the rock formation, cracks will be formed around the fracture hole, and finally the nitrogen gas will be recovered and recycled. This method combines the advantages of fatigue weakening, cold shock and gasification expansion. On the one hand, it relies on the increasing volume of the gas-liquid two-phase flow pressure group formed in the limited space of the borehole to cause a sudden drop in the internal temperature of the rock formation to induce thermal stress; On the other hand, the pulsating injection method enables the nitrogen gas-liquid two-phase flow to flow rapidly into the fracture, accelerates the crack expansion rate, and finally realizes the effective collapse of the roof strata. The method has the advantages of simple and convenient construction, low cost and wide application range.

Description

A Fracture Weakening Method for Coal Seam Hard Roof

technical field

The invention relates to a cracking and weakening method for a hard roof of a coal seam, which is mainly suitable for the effective caving work of a dense and hard roof layer rich in clay matrix, and can combine the weakening characteristics of pulsation fatigue, the low-temperature cold impact of liquid nitrogen, and the gas The advantages of the three aspects of the fracturing effect realize the high-efficiency caving of the roof rock formation.

Background technique

In China, hard roofs with high strength, large thickness and good integrity are widely distributed in various mining areas. With the mining of coal resources and the gradual advancement of the working face, the area of the roof overhang formed inside the stope is gradually increasing. If it cannot be effectively collapsed, the support strength and difficulty of the stope area will inevitably be increased. During the advancing process of the working face, the periodic pressure or the initial pressure step distance of the hard _roof stratum is continuously increasing, and a large amount of energy is continuously accumulated. When the self- _weight of G exceeds the ultimate strength _σus of the roof stratum, the overall fracture and collapse will occur, which will easily induce hurricane accidents in the limited stope space, damage the roadway facilities and cause casualties, and affect the normal production progress of the mine.

At present, in view of the caving of the hard and dense roof strata, a series of pre-fracturing methods are often used in the traditional sense to force the roof to cause cracks in the dense and integral roof strata to cause massive collapse and avoid hurricane accidents. . Common pre-fracturing methods include deep-hole blasting, high-pressure hydraulic fracturing, and water injection weakening. These technologies all have certain limitations. For example, the shock waves generated by deep hole blasting can easily cause stress disturbances in coal and rock mass, often accompanied by explosion rejection or squibs; high-pressure hydraulic fracturing and water injection weakening consume a lot of water resources , water resources added with chemical reagents are more likely to cause pollution. In addition, when the roof rock layer contains a large amount of clay, it is easy to cause the clay to absorb water and swell, and the effect of cracking and caving cannot be achieved. Therefore, for the effective collapse of clay-rich roof strata, a low-cost, easy-to-operate, and effective fracturing method is urgently needed to avoid hurricane accidents caused by large-scale collapse of hard roofs.

Contents of the invention

Purpose of the invention: The present invention is aimed at the problem of effective caving of the hard roof strata rich in clay matrix, and proposes a cracking and weakening method for the hard roof of the coal seam. Weakening fracturing is performed on the roof rock formation.

In order to achieve the above object, the present invention adopts the following technical scheme: a method for cracking and weakening of a hard roof of a coal seam, comprising the following steps:

a. Drilling: When the mining face moves forward for a certain distance, use the drilling rig to drill multiple cracking holes and pilot holes into the difficult-to-collapse hard roof strata in the stope area. Cut wedge-shaped slots with hydraulic slotting device;

b. Preparation of liquid nitrogen: Connect the air compressor to the cooling unit through the exhaust pipeline, install a negative pressure fan on the exhaust pipeline, compress the air through the air compressor, and cool the compressed air through the cooling unit to liquefy, and then form liquid nitrogen. Then store the liquid nitrogen in the liquid nitrogen storage tank;

c. Hole sealing: first insert the heat insulating sleeve into the cracking hole, and then insert the gas injection high-pressure expansion hole sealing device into the insulating sleeve. Between the inner wall of the insulation casing and the outer wall of the gas injection high-pressure expansion hole sealer, the ethylene glycol antifreeze is used to bond and seal. Into the fracturing hole, install a return air stop valve on the return air pipe;

d. Pulsating injection of liquid nitrogen: connect the liquid nitrogen storage tank with the liquid injection pipe, install a liquid injection pump, an equal volume shunt and a pressure gauge on the liquid injection pipe, connect the liquid injection pipe with the cracking pipe through a one-way valve, and close Return air stop valve, open the liquid supply valve on the liquid nitrogen storage tank, inject the liquid nitrogen in the liquid nitrogen storage tank into the fracturing hole through the liquid injection pipe and the fracturing pipe, when the pressure gauge value P>2.5MPa, pass The frequency regulator adjusts the motor frequency of the liquid injection pump to 4Hz, and injects liquid nitrogen into the fracturing hole for ten minutes, and then gradually increases the motor frequency of the liquid injection pump through the frequency regulator. Inject liquid nitrogen into the fracturing hole for ten minutes, until the pressure gauge value P<0.5MPa, close the liquid injection pump and liquid supply valve;

e. Nitrogen gas recovery: Connect the gas return pipe to the pumping pipeline. When the pulsating liquid nitrogen injection process is over, open the gas return shut-off valve, and extract the nitrogen gas to the extraction pipeline through a negative pressure fan to perform the liquid nitrogen preparation process.

f. As the mining face continues to move forward, follow the above steps a to e in turn to make the roof strata fall effectively.

Further, the distance between the fracturing hole and the guide hole is 4-5m.

Further, the angle of the fracturing hole and the guide hole is inclined upwards by 30-60° along the gob direction, the hole depth is 8-10m, and the hole diameter is 30-35cm.

Further, the cracking pipe, liquid injection pipe, and gas return pipe are all made of antifreeze cracking seamless steel pipes, and the inside of the antifreeze cracking seamless steel pipes is covered with rock wool, asbestos or glass fiber with thermal insulation properties.

Further, the temperature control range of the cooling unit is -250--10°C.

Further, an antirust agent is added to the ethylene glycol antifreeze.

Further, the air pressure control range of the negative pressure fan is -0.8MPa～-1.2MPa, and an air filter is arranged at the air inlet of the negative pressure fan to prevent rock formation debris from entering the negative pressure fan and malfunctioning.

Further, in step d, the frequency of the motor of the infusion pump is increased by 4 Hz each time.

Beneficial effects: the above-mentioned technical solution is able to organically couple the three aspects of pulsation fatigue weakening characteristics, liquid nitrogen low-temperature cold shock effect, and gas cracking effect, and then solve the problem of hard and integral roof strata rich in clay matrix. The fracturing medium used in the method has a wide range of sources, accounting for 78% of the atmosphere. The gaseous nitrogen is transformed into liquid nitrogen by using an air compressor and a refrigerating unit, and the nitrogen after the action can be recycled without causing environmental pollution. In terms of the mechanism of action, on the one hand, relying on different injection frequencies, the liquid nitrogen will cause different degrees of cold impact on the roof rock formation, resulting in a sudden drop in the temperature inside the rock formation, forming a certain temperature gradient in the action area, and weakening under the mechanism of fatigue accumulation and temperature stress coupling. The strength of the rock formation itself; on the other hand, the gasification of liquid nitrogen continuously produces nitrogen gas, which forms an increasing volume of gas-liquid two-phase mixed pressure group in the limited space of the drill hole, and finally exceeds the tensile strength of the rock formation to form cracks. In addition, with the continuous extension of the fracture, the pulsating injection method makes the gas-liquid two-phase flow flow into the fracture rapidly, accelerates the expansion rate of the fracture, and finally realizes the effective collapse of the roof strata. The method has the advantages of simple and convenient construction, low cost and wide application range.

Description of drawings

Fig. 1 is the schematic diagram of the cracking weakening method of hard roof of coal seam of the present invention;

Fig. 2 is the schematic diagram of the drilling hole caused by the hard roof of the coal seam;

Fig. 3 is a schematic cross-sectional view of an insulating sleeve;

In Fig. 1: 1—refractory hard roof rock formation; 2—fracture hole; 2-1 wedge-shaped slot; 3—pilot hole; 4—fracture tube; ; 7—pressure gauge; 8—one-way valve; 9—injection pipe; 10—equal flow divider; 11—injection pump; - Liquid nitrogen storage tank; 16 - Liquid nitrogen; 17 - Air return pipe; 18 - Exhaust pipeline; 19 - Negative pressure fan; 20 - Cooling unit; 21 - Air compressor;

In Fig. 2: 1—refractory hard roof stratum; 2—fracture hole; 3—pilot hole; 22—mining face; Ⅰ—goaf; Ⅱ—coal seam; Ⅲ—roadway; Ⅳ—stope area;

In Fig. 3: 5-1—tube wall; 5-2—tube lumen.

detailed description:

The present invention will be further explained below in conjunction with the accompanying drawings.

As shown in Figures 1 and 2, a kind of coal seam hard roof fracturing weakening method of the present invention comprises the following steps:

a. Drilling: When the mining face 22 moves forward for a certain distance, use a drilling rig to drill a plurality of cracking holes 2 and pilot holes 3 inside the hard roof stratum 1 in the stope area, and drill holes 2 and pilot holes 3 Spaced apart from each other, a wedge-shaped slot 2-1 is cut out at the top of the fracturing hole 2 using a hydraulic slotting device;

b. Preparation of liquid nitrogen: connect the air compressor 21 to the cooling unit 20 through the air extraction pipeline 18, install a negative pressure fan 19 on the air extraction pipeline 18, compress the air through the air compressor 21, and pass the compressed air through the cooling unit 20 cooling and liquefaction, and then forming liquid nitrogen 16, and then storing the liquid nitrogen 16 in the liquid nitrogen storage tank 15;

c. Hole sealing: first insert the heat insulating sleeve 5 into the fracturing hole 2, as shown in Figure 3, the pipe wall 5-1 of the heat insulating sleeve 5 is corrugated, and then extend the gas injection high-pressure expansion sealing device 6 into the Into the lumen 5-2 of the heat insulating sleeve 5, the penetration depth is less than the length of the heat insulating sleeve 5, between the outer wall of the heat insulating sleeve 5 and the inner wall of the fracturing hole 2, between the inner wall of the insulating sleeve 5 and the gas injection high pressure expansion hole sealing device 6. The outer walls are bonded and blocked by ethylene glycol antifreeze. The ethylene glycol antifreeze is added with antirust agent. The ethylene glycol antifreeze can penetrate into the inner wall of the fracturing hole 2 to seal the cracks on the wall of the drilled hole, thereby To ensure airtightness, finally pass the fracturing pipe 4 and the gas return pipe 17 through the gas injection high-pressure expansion sealing device 6 and extend into the fracturing hole 2, and install the return gas stop valve 14 on the gas return pipe 17;

d. Pulsating injection of liquid nitrogen: connect the liquid nitrogen storage tank 15 with the liquid injection pipe 9, install the liquid injection pump 11, the equal volume shunt 10 and the pressure gauge 7 on the liquid injection pipe 9, and pass the liquid injection pipe 9 through the one-way valve 8 is connected to the cracking tube 4, closes the gas return stop valve 14, opens the liquid supply valve 13 on the liquid nitrogen storage tank 15, and injects the liquid nitrogen 16 in the liquid nitrogen storage tank 15 through the liquid injection tube 9 and the cracking tube 4 In the fracturing hole 2, when the value of the pressure gauge 7 is P>2.5MPa, adjust the motor frequency of the injection pump 11 to 4Hz through the frequency regulator 12, and inject liquid nitrogen into the fracturing hole 2 for 16 minutes, and then pass the frequency regulator 12 Increase the motor frequency of the liquid injection pump 11 step by step. Preferably, the motor frequency of the liquid injection pump 11 is increased by 4 Hz each time, that is, gradually increase the motor frequency of the liquid injection pump 11 to 8Hz, 12Hz, 16Hz, 20Hz... …, every time the frequency of the motor of the liquid injection pump 11 is increased, liquid nitrogen is injected into the fracturing hole 2 for 16 minutes. As a result, the internal temperature of the rock formation drops sharply, and a certain temperature gradient is formed in the impacted area of the rock formation, which weakens the strength of the rock formation itself under the coupling mechanism of fatigue accumulation and temperature stress. The increased gas-liquid two-phase mixed pressure group eventually exceeds the tensile strength of the rock formation to form cracks. As the cracks continue to extend, the pulsating injection method makes the gas-liquid two-phase flow quickly flow into the cracks, accelerating the crack expansion rate, and finally To realize the effective collapse of the rock formation, the value of the pressure gauge 7 decreases with the collapse of the rock formation, and when the value of the pressure gauge 7 is P<0.5MPa, close the liquid injection pump 11 and the liquid supply valve 13;

e. Nitrogen gas recovery: connect the air return pipe 17 to the extraction pipeline 18. After the process of pulsating injection of liquid nitrogen is over, open the return gas shut-off valve 14, extract the nitrogen gas through the negative pressure fan 19 to the extraction pipeline 18, and perform liquid nitrogen extraction. Nitrogen production process.

f, as shown in Figure 2, the mining face 22 moves forward continuously along the roadway, and after the mining face 22 moves forward for a certain distance, a block of stope area is formed, and the back of the stope area is a goaf. The mining work is constantly moving forward, and the roof stratum is effectively stepped down according to the above steps a to e.

In this embodiment, the distance between the cracking hole 2 and the guide hole 3 is 4-5m, and the inclination angle between the cracking hole 2 and the guide hole 3 is 30-60°, the hole depth is 8-10m, and the hole diameter is 30-60°. 35cm; the cracking pipe 4, the liquid injection pipe 9, and the air return pipe 18 are all made of antifreeze cracking seamless steel pipes, and rock wool, asbestos or glass fibers containing thermal insulation properties are set inside the antifreeze cracking seamless steel pipes; the cooling The temperature control range of the unit 20 is -250 to -10°C; the air pressure control range of the negative pressure fan 19 is -0.8MPa to -1.2MPa, and the relevant parameters of the fan are specifically: the air volume is 3000m ³ /h, and the speed is 500 Turn/min, the fan blade diameter is 800mm, and an air filter is arranged at the air inlet of the negative pressure fan 19 to prevent rock formation debris from entering the negative pressure fan 19 to break down.

The above is only a preferred embodiment of the present invention, it should be pointed out that, for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications can also be made. It should be regarded as the protection scope of the present invention.

Claims (8)

1. a kind of coal seam tight roof fracturing method for weakening, it is characterised in that comprise the following steps：

A, drill：After stope (22) elapses a segment distance forward, collapsed hard top to the difficulty in stope region using rig Multiple fracturing holes (2) and pilot hole (3) are drilled through inside slate layer (1), fracturing hole (2) and pilot hole (3) are spaced, in fracturing Wedge-shaped slot (2-1) is cut out using hydraulic slotted liner technique device in hole (2) top；

B, prepared by liquid nitrogen：Air compressor (21) is connected by exhaust pipe (18) with cooling unit (20), exhaust pipe (18) negative-pressure air fan (19) is installed on, is compressed air by air compressor (21), compressed air via cooler Group (20) cooling liquid, and then liquid nitrogen (16) is formed, then liquid nitrogen (16) is stored in liquid nitrogen storage tank (15)；

C, sealing of hole：First insulation casing (5) is inserted in fracturing hole (2), then the high compression swelling hole packer (6) of gas injection is extend into thermal insulation In sleeve pipe (5), the length that depth is less than insulation casing (5) is stretched into, between insulation casing (5) outer wall and fracturing hole (2) inwall, absolutely Carry out cohering closure by ethylene glycol antifreeze between thermal sleeve (5) inwall and high compression swelling hole packer (6) outer wall of gas injection, most Fracturing pipe (4) and muffler (17) through the high compression swelling hole packer (6) of gas injection and are extend into fracturing hole (2), muffler afterwards (17) return-air stop valve (14) is installed on；

D, pulsation injection liquid nitrogen：Liquid nitrogen storage tank (15) is connected with liquid injection pipe (9), on liquid injection pipe (9) install topping-up pump (11), etc. Current divider (10) and pressure gauge (7) are measured, liquid injection pipe (9) is connected by one-way cock (8) with fracturing pipe (4), return-air is closed and cuts Only valve (14), the supplying valve (13) on liquid nitrogen storage tank (15) is opened, the liquid nitrogen (16) in liquid nitrogen storage tank (15) is passed through into liquid injection pipe (9) it is injected into fracturing pipe (4) in fracturing hole (2), as pressure gauge (7) numerical value P>During 2.5MPa, it will be noted by frequency modulator (12) The electric machine frequency of liquid pump (11) is adjusted to 4Hz, and injection liquid nitrogen (16) ten minutes in fracturing hole (2), then passes through frequency modulator (12) electric machine frequency of topping-up pump (11) is gradually heightened, often heightens the electric machine frequency of a topping-up pump (11) just to fracturing hole (2) Middle injection liquid nitrogen (16) ten minutes, until pressure gauge (7) numerical value P<During 0.5MPa, topping-up pump (11) and supplying valve (13) are closed；

E, nitrogen recycling：Muffler (17) is connected to exhaust pipe (18), after pulsation injection liquid nitrogen process terminates, opened back Gas stop valve (14), by nitrogen by negative-pressure air fan (19) extraction to extraction pipeline (18), perform liquid nitrogen preparation process.

F, constantly elapsing forward with stope, successively according to above-mentioned steps a to e, make roof strata carry out effectively across Fall.

A kind of 2. coal seam tight roof fracturing method for weakening according to claim 1, it is characterised in that the fracturing hole (2) spacing between pilot hole (3) is 4~5m.

A kind of 3. coal seam tight roof fracturing method for weakening according to claim 2, it is characterised in that the fracturing hole (2) it is inclined upwardly 30~60 °, hole depth 8-10m, aperture 30-35cm along goaf direction with pilot hole (3) angle.

A kind of 4. coal seam tight roof fracturing method for weakening according to claim 1, it is characterised in that the fracturing pipe (4), liquid injection pipe (9), muffler (17) use frost-cracking-preventing seamless steel pipe, are cased with inside frost-cracking-preventing seamless steel pipe containing adiabatic special Rock wool, asbestos or the glass fibre of property.

A kind of 5. coal seam tight roof fracturing method for weakening according to claim 1, it is characterised in that the cooling unit (20) temperature controlling range is -250~-10 DEG C.

6. a kind of coal seam tight roof fracturing method for weakening according to claim 1, it is characterised in that the ethylene glycol is prevented Freeze in liquid and be added with antirust agent.

A kind of 7. coal seam tight roof fracturing method for weakening according to claim 1, it is characterised in that：The negative-pressure air fan (19) blast control range is -0.8MPa~-1.2MPa, and an air cleaner is arranged in negative-pressure air fan (19) air intake vent, Prevent rock stratum disintegrating slag enters in negative-pressure air fan (19) from breaking down.

A kind of 8. coal seam tight roof fracturing method for weakening according to claim 1, it is characterised in that：It is described in step d The electric machine frequency of topping-up pump (11) heightens 4Hz every time.